Pumping system

ABSTRACT

A high pressure pumping system in which a first pump delivers a medium to a discharge port and to a second pump which subsequently delivers the medium to the discharge port.

BACKGROUND OF THE INVENTION

This invention relates to a system for pumping liquids at highpressures.

Various pumps exist for different applications. Hose pumps are commonlyused for pumping dirty, viscous and abrasive slurries, waste sludge andso on. Worm pumps are employed primarily in the food industry forpumping semi-viscous liquids with a relatively fine grain structure.Bladder and diaphragm pumps find application particularly in the miningindustry although they are also employed in the food and chemicalindustries. These pumps tolerate chemicals and abrasives and can handlerelatively large solids.

Multi-stage centrifugal pumps are usually encountered in the miningindustry for dewatering applications, in water treatment plants and soon. These pumps have a relatively poor abrasion resistance.

The aforementioned types of pumps, in general, are limited in respect ofpressure capabilities. Although these pumps can operate at high deliveryrates their efficiencies are strongly reduced when they are called uponto operate at higher pressures.

By way of contrast a positive displacement piston-type pump can generatea high pressure and flow rate with good efficiency but it suffers frompoor abrasion and chemical resistance. Another adverse factor is thatthis type of pump has a pulsating delivery. Instantaneous and frequentflow fluctuations in liquid delivery structures, under high pressure,may fatigue the structures in short periods of time, causing unexpecteddamage and high repair expenses, and can pose severe safety hazards. Apressure accumulator can be employed to make the flow rate more or lessconstant but, at high flow volumes and high pressures, especially whenpumping abrasive and corrosive liquids, this type of accumulator isexpensive and calls for high maintenance.

US patent No. 2006/0239840A1 describes a combination of a bladder andpiston pump. Reciprocating hydraulic pistons act as a power source via amechanical linear crank action from a rotating cam which is driven by aprime mover. A bladder or bellows is used to pump a liquid. Although thepump can operate at a relatively high pressure, and can pump viscous,abrasive and corrosive liquids, it is, in the applicant's opinion,bulky, complicated, expensive and difficult to maintain.

In general, reciprocating piston, bladder or bellows pumps provide apulsing delivery flow, yet multiple pumping units do reduce the pressureand flow fluctuations. Each pump unit requires two non-return valves,one for suction and one for delivery. These are costly, high wearservice items.

An object of the present invention is to provide a system which canoperate efficiently at a very high pressure for the pumping of liquidwhich may be viscous, abrasive, acidic or contain particulate material,in a substantially constant, non-pulsating delivery flow, and which usesa reduced number of service items. This type of pumping system findsapplication; inter alia, in the pumping of slurries, in water jetting,oil well drilling, ground solidification, dewatering and in firefighting. These applications are exemplary only and are non-limiting.

SUMMARY OF THE INVENTION

The invention provides a liquid pumping system which includes:

-   (a) a liquid transfer pump arrangement which includes a liquid inlet    port, a liquid discharge port, a first pump chamber with a first    maximum volume, a first non-return valve connected to and between    the liquid inlet port and the first pump chamber, a first control    device for pumping liquid from the first pump chamber, a second pump    chamber with a second maximum volume, wherein the second maximum    volume is at least half the size of the first maximum volume, the    second pump chamber being connected to the liquid discharge port, a    second non-return valve connected to, and between, the first pump    chamber and the second pump chamber and a second control device for    pumping liquid from the second pump chamber,-   (b) a hydraulic fluid constant flow pump, and-   (c) control structure which, responsive to liquid flow rates from    each pump chamber, directs hydraulic fluid to the first and second    control devices at respective controlled rates whereby, upon    actuation of the first and second control devices, in a cyclical    manner:    -   (1) liquid is expelled from the first pump chamber through the        second non-return valve:        -   (1.1) at a controlled delivery rate to the liquid discharge            port, and        -   (1.2) into the second pump chamber, and, thereafter,    -   (2) liquid is directed from the liquid inlet port through the        first non-return valve into the first pump chamber, and liquid        is expelled from the second pump chamber at said controlled        delivery rate to the liquid discharge port.

The pump chambers may take on any appropriate form. In one example ofthe invention the first pump chamber is formed by a first cylinder and afirst piston which is reciprocally movable inside the first cylinder.The second pump chamber is similarly formed from a second cylinder and asecond piston.

In each case each control device causes movement of the respectivepiston. By way of non-limiting examples each control device may, itself,comprise a respective piston and cylinder assembly, a lead screw or anyequivalent adjustment mechanism.

The desired relationship between the first maximum volume and the secondmaximum volume may be achieved in different ways. For example the firstcylinder may have a cross-sectional area which is less than two timesthe cross-sectional area of the second cylinder. Alternatively, if thecross-sectional areas of the cylinders are substantially the same, thestroke of the first piston may be less than two times the stroke of thesecond piston. Another possibility is to vary the relativecross-sectional areas of the cylinders and the strokes of the pistons toensure that a constant flow is delivered without pressure fluctuations.

When the first pump chamber is full both pistons momentarily executedelivery strokes. This allows a smooth transition between delivery fromthe pistons in that the first piston can accelerate slowly and thesecond piston can be smoothly slowed to be stationary before reversingfor its filling cycle.

In another form of the invention each pump chamber is formed by arespective bellows or a diaphragm such as a bladder. The bellows, orbladder, can then be changed from an extended or retracted mode by therespective control device and then enlarged to an operativeconfiguration. If a bellows is used, the liquid medium to be pumped maybe directed into an interior of the bellows, and the hydraulic powermedium may be directed to a space between a wall of a cylinder and thebellows i.e. to retract the bellows. Alternatively the hydraulic powermedium may be directed to inside the bellows to extend the bellows. Themedium to be pumped is then displaced from a space between a cylinderand the bellows as the bellows is expanded. Thus the chamber may beinside, or outside of, the bellows.

In both cases, the internal pressures of the bellows must be keptpositive, otherwise the bellows will collapse. This is done with thecontrol structure using hydraulic throttling in main lines for thehydraulic power medium and a control cylinder. The control cylinder mayeither assist the bellows to extend, or restrain extension of thebellows, in a controlled way, so as to maintain a positive pressureinside the bellows. The bellows may be supported by an extension of thecontrol cylinder. In this case the cross-sectional area of the bellowson the cylinder side is always slightly smaller. Typical ratings forcommercially available bladders and bellows are 8 bar internal pressureand 25 bar burst limit. The pressure differential between the inner andouter surfaces of the bellows should therefore be controlled to ensureeffective operation.

Each control device may be any suitable mechanism e.g. a small doubleacting control cylinder or a lead screw, preferably with a trapezoidalthread so that the thread can exert a pushing and a pulling forceeffectively. A combination of the aforegoing may also be employed. Ahydraulic cylinder is preferred as it is small in size, yet capable ofproviding substantial force. A measurement of the hydraulic fluid flowinto or out of the control cylinder provides accurate feedback for othercontrol structures, such as a PLC, hydraulic valves, and so on.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by way of examples with reference tothe accompanying drawings in which:

FIG. 1 shows a liquid pumping system which includes a liquid transferpump arrangement which is based on the use of cylinders and pistons,according to a first form of the invention,

FIG. 2 shows a second form of the invention comprising a liquid transferpump arrangement which is based on the use of bellows or diaphragms,

FIG. 3 shows a variation of the FIG. 2 system in that bellows ordiaphragms, included in the liquid transfer pump arrangement, areaxially aligned and not separated from each other as is the case in FIG.2, and

FIG. 4 illustrates charge and discharge curves over a pump cycle.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 schematically shows a liquid pumping system 10 according to afirst form of the invention which includes, enclosed in each case indotted outline, a liquid transfer pump arrangement 12, a hydraulic fluidconstant flow pump arrangement 14, and control structure 16.

The liquid transfer pump arrangement 12 has two principal componentsnamely a first liquid delivery arrangement 20 and a second liquiddelivery arrangement 22.

The first liquid delivery arrangement 20 includes a first cylinder 24with a first piston 26 which, together, define a first pump chamber 28.A first control device 30 which, itself, comprises a piston 32 and acylinder 34, is used to cause controlled movement of the piston 26.Similarly the second liquid delivery arrangement 22 includes a secondcylinder 40, a second, delivery piston 42, and a second control device44 which is constituted by a piston 46 and a cylinder 48 which operateon the delivery piston 42.

The second piston and cylinder define a second pump chamber 50.

Liquid which is to be pumped is held in a source 52 which is connectedvia an inlet port 54 and a first non-return valve 56 to the first pumpchamber 28.

A second non-return valve 60 is connected to and between the first pumpchamber 28 and the second pump chamber 50, and to a discharge port 66.An accumulator 68 connected between the inlet port 54 and the firstnon-return valve 56 is used to absorb pressure or flow variations in theliquid flowing from the source 52 to the first non-return valve.

The constant flow hydraulic fluid arrangement 14 includes a motor 70which drives a pump 72 which delivers hydraulic fluid at a constantrate. The motor is also used to drive a fan 74 which provides a coolingstream of air to a heat exchanger 76 used to cool hydraulic fluid.Proportional control valves 78 and 80, included in the control structure16, are used to regulate the flow of hydraulic fluid from the pump 72 tothe liquid transfer pump arrangement 12. The pressurization of thecontrol devices 30 and 44 is performed from the main pump 72, or couldbe performed with a separate, small, on-demand pump 73.

Fluid flow to the control devices takes place via pressure regulatorvalves 82 and 84, a change over valve 86, and flow meters 88 and 90respectively.

An end of the stroke of each control cylinder (in the respective devices30 and 44) is detected with respective switches 91 and 92. Datagenerated by the operation of the switches is supplied to the controlstructure which is calibrated during each return stroke of each of thecylinders by means of a microprocessor or programmable logic controller(PLC) 100 which is included in the control structure.

When the pistons 26 and 42 are extending or retracting, flow counts fromthe flow meters 88 and 90 provide feedback to the PLC 100 which controlsthe hydraulic system and which ensures a constant output flow from thedischarge port 66. Additionally, pressure transducers P₁ to P₄ monitorthe pressures in the chambers, and feed data thereon to the PLC 100which, in response to this data, adjusts the hydraulic system and thepressures in the control cylinders to maintain optimum pressurebalances.

The pumping system includes at least one pressure filter 96 for thehydraulic fluid delivered by the pump 72.

The maximum volume of the second pump chamber 50 is preferably at leasthalf the size of the maximum volume of the first pump chamber 28. Thiscan be achieved in various ways. For example, the cross sectional areaof the cylinder 24 may be at least two times the cross sectional area ofthe cylinder 40. Alternatively, the strokes of the pistons 26 and 42 canbe varied. It is also possible to use a combination of different strokelengths with different cross-sectional areas to ensure that the maximumvolume of the second pump chamber is at least half the size of themaximum volume of the first pump chamber.

If the filling cycle for the first chamber is fast, then the secondchamber could be correspondingly small and would act only to dischargeduring a short period of time as the first chamber is being filled.This, however, is not beneficial because high pressure spikes would beproduced in the inlet port 54.

In use of the pumping system, liquid from the inlet port 54 flowsthrough the first non-return valve 56 into the first pump chamber 28.The first piston 26 is retracted by the pumping action of the firstcontrol device 30 which operates, under the control of the controller100, using energy from hydraulic fluid delivered by the pump 72. Thisdescription applies when the pump unit is self-priming. If the inletline is pressurized then the piston retraction is assisted by the inletpressure and the control device only regulates the filling rate and thespeed.

Once the chamber 28 is fully charged the piston 26 reverses directionand discharges liquid from the chamber 28 through the second non-returnvalve 60. Liquid cannot flow to the source due to the action of thefirst non-return valve 56. The controller 100 regulates the flow ratefrom the chamber 28 and the pressure of the liquid delivered from thischamber. The liquid is delivered, firstly, to the discharge port 66 and,secondly, into the second pump chamber 50. The volume of liquid whichflows into the chamber 50, and the rate at which this liquid flows, areregulated by the second control device 44 i.e. by retraction of thepiston 42. When the piston 42 is retracting, the hydraulic oil behind itis regenerating and adds into the fluid delivery supply from the pump72, speeding up the discharge stroke of the piston 26.

As the maximum volume of the second pump chamber 50 is at least half thesize of the maximum volume of the first pump chamber 28, liquidcontinues to flow from the first pump chamber 28 to the discharge port66 once the second pumping chamber 50 is full. At this point the piston42 is reversed and liquid is then expelled from the second chamber 50 tothe discharge port 66. Liquid cannot return to the first pump chamber 28because of the blocking action of the second non-return valve. Thepistons 26 and 42 momentarily and simultaneously perform respectivedischarge strokes. When the piston 26 stops, the non-return valve 60closes and the piston 42 speeds up on its delivery stroke. The piston 26then starts its suction stroke. The rate at which liquid is deliveredfrom the second pump chamber 50 is regulated by the controller 100, andby the supply of hydraulic fluid from the fixed displacement pump 72.The delivery of liquid from the first pump chamber 28 is correspondinglyreduced, ultimately to zero, to ensure that the delivery rate throughthe port 66 is kept effectively constant.

As the piston 42 advances the piston 26 is retracted so that the firstpump chamber 28 is recharged. The piston 26 is reversed shortly beforethe piston 42 reaches the end of its delivery stroke. To compensate forthe opening and closing times of the non-return valves and to achieve apulseless delivery shift between the pump chambers, the pistons 26 and42, as noted, perform momentarily and simultaneously, respective liquiddelivery strokes.

The non-return valves 56 and 60 are not used for throttling liquid flow.These valves are piloted fully open or fully closed, according torequirement. This characteristic effectively eliminates “sand blasting”on the components of the valves and increases the life expectancy of thevalves. Thus the non-return valves only control liquid flow into or outof the first pump chamber 28.

The aforementioned process is repeated in a cyclical manner so that aconstant liquid flow at a desired operating pressure is achieved. Thehydraulic fluid is separated from the liquid which is pumped and it ispossible therefore to configure the cylinders 24 and 40, and the pistons26 and 42, respectively, so that viscous, abrasive and acidic liquidscan be pumped.

Pumping takes place at the high efficiencies and pressures associatedwith positive displacement piston pumps, but at an effectively constantflow rate. It is envisaged that a pumping system of the kind describedcan operate at pressures of up to 40 MPa with a continuous duty cycleand at a flow rate of up to 10000 litres per hour, at an efficiencyexceeding 90%. These performance characteristics can be achieved usingcomponents which, for practical reasons, can be considered to bestandard components. A fixed displacement hydraulic pump may be replacedwith a variable displacement pump in cases where the pumping rate mustbe adjustable. A reduction of the displacement does however constitute areduction of pump efficiency.

Despite the benefits of the arrangement shown in FIG. 1 the pumpchambers 28 and 50 are constituted by relatively large, and henceexpensive, cylinders and corresponding pistons. FIG. 2 illustrates amodified pumping system 10A which has many similarities to the system 10and which, for this reason, is not fully described. Where applicablelike reference numerals are used to designate like components.

The cylinder 24 and piston 26 are replaced, respectively, by a vessel24A and a bellows or diaphragm 26A. Similarly, the cylinder 40 isreplaced by a vessel 40A, and the piston 42 is replaced by a bellows ordiaphragm 42A. Control devices 30A and 44A act directly on therespective bellows 26A and 42A. The bellows 42A has an effective maximumvolume which is at least half the size of the maximum volume of thebellows 26A. The system 10A functions in a manner which is similar tothat described in connection with FIG. 1. However, the use of thebellows or diaphragms means that an expensive and bulky piston andcylinder arrangement is not required. Additionally, mechanical sealswhich are subject to wear, under abrasive conditions, are eliminated.

FIG. 3 shows another system 10C, which has substantial similarities tothe system 10A. With the system 10A, the bellows 26A and 42A are locatedin separately constructed and spaced apart vessels 24A and 40Arespectively. In the system 10C the bellows are in line with each other.Volumes 28B and 50B on outer sides of the bellows are linked via a portarrangement 106 which facilitates fluid transfer between these volumes.In other respects, however, the respective control devices 30A and 44Aare used, essentially as has been described, to control expansion orretraction (collapse) of the bellows. The system 10C preferably includespressure transducers P₁ to P₄, similar to those shown in FIG. 1, whichfunction to monitor pressure balances in the system and to ensure thatappropriate data is fed to the PLC 100 which, in turn, acts to maintainoptimum pressure balances within the system.

A preferred mounting orientation of the designs in FIG. 2 and FIG. 3, isvertical, so that the mass of the pistons and the mass of the bellows donot contribute to uneven wear on, and premature failure of, thecomponents. If concrete or heavy solids are to be pumped, the pumpchambers and non-return valve locations must be altered accordingly, sothat solids do not start building up inside the pump chambers.

FIG. 4 graphically depicts aspects of the pumping sequence referred to,over a pump cycle T with a cycle time of, say, 4 seconds. Assume thefirst chamber 28 has a maximum volume of 20 litres and that the secondchamber 50 has a maximum volume of 11.5 litres. The first chamber isrecharged over an interval from T1 to T2 and discharges from T3 to T4.The second chamber is recharged during an interval from T5 to T6 anddischarges from T6 to T5.

The pump chambers simultaneously discharge over the intervals T3 to T5and from T6 to T4.

A dotted line D represents the net outflow from the first chamber i.e.8.5 litres (equal to 20-11.5 litres).

The discharge rate per cycle is thus 11.5 plus 8.5 equals 20 litres.

With a cycle time of 4 seconds, there are fifteen cycles per minute. Thedischarge rate is thus 15×20=300 litres per minute. The discharge rateis continuous and constant because of the use of the fixed displacementpump 72.

When the bellows are used the speeds of the pistons adjust automaticallyto match the hydraulic fluid flow rate from the pump 72. During thebrief intervals that the pistons work simultaneously the speed of eachpiston alters accordingly and the discharge flow rate is maintainedeffectively at a constant value.

The flow and pressure fluctuations in the incoming low pressure liquidport 54 can be minimized by suitably dimensioning the chambers 28 and50. If the volume of the discharge chamber 50 is increased, the periodtaken to re-charge the inlet chamber 28 is increased. The pressureaccumulator 68, see FIG. 1, is used to level the intake flowfluctuations and pressure spikes.

If the input flow rate is required to stay reasonably constant, a third,liquid delivery arrangement could replace the accumulator 68. Thisdelivery arrangement is not shown for it would be of similar design tothe high pressure arrangements 20 and 22. The liquid deliveryarrangement and the control device would then be linked to the PLC 100and would be powered by the return flow from the high pressure pumpunit.

1. A liquid pumping system which includes: (a) a liquid transfer pumparrangement (12) which includes a liquid inlet port (54), a liquiddischarge port (66), a first pump chamber (28) with a first maximumvolume, a first non-return valve (56) connected to and between theliquid inlet port (54) and the first pump chamber (28), a first controldevice (30) for pumping liquid from the first pump chamber (28), asecond pump chamber (50) with a second maximum volume, wherein thesecond maximum volume is at least half the size of the first maximumvolume, the second pump chamber (57) being connected to the liquiddischarge port (66), a second non-return valve (67) connected to, andbetween, the first pump chamber (28) and the second pump chamber (50)and a second control device (46) for pumping liquid from the second pumpchamber (50), (b) a hydraulic fluid constant flow pump (72), and (c)control structure (100) which, responsive to liquid flow rates from eachpump chamber (28, 50), directs hydraulic fluid to the first and secondcontrol devices (30, 46) at respective controlled rates whereby, uponactuation of the first and second control devices (30, 46), in acyclical manner: (1) liquid is expelled from the first pump chamber (28)through the second non-return valve (60): (1.1) at a controlled deliveryrate to the liquid discharge port (66), and (1.2) into the second pumpchamber (50), and, thereafter, (2) liquid is directed from the liquidinlet port (54) through the first non-return valve into the first pumpchamber (28), and liquid is expelled from the second pump chamber (50)at said controlled delivery rate to the liquid discharge port (66).
 2. Apumping system according to claim 1 wherein the first pump chamber (28)is formed by a first cylinder (24) and a first piston (26) which isreciprocally movable inside the first cylinder (24), and the second pumpchamber (50) is formed by a second cylinder (40) and a second piston(46) which is reciprocally movable inside the second cylinder (40).
 3. Apumping system according to claim 2 wherein, in response to the controlstructures (30, 44, 33A, 44A, 88, 90 and 100) the first piston (26) andthe second piston (42) simultaneously execute delivery strokes toprovide a pulseless delivery flow from the discharge port (66) during apumping cycle.
 4. A pumping system according to claim 1 wherein eachpump chamber (28A, 28B; 50A, 50B) is partly formed by a respectivebellows or diaphragm (26A, 26B; 42A, 42B).
 5. A pumping system accordingto claim 4 wherein the liquid medium to be pumped is directed into aninterior of the bellows, and the hydraulic power medium is directed to aspace between a wall of a cylinder and the bellows.
 6. A pumping systemaccording to claim 4 wherein the hydraulic power medium is directed intoan interior of the bellows and the medium to be pumped is then displacedfrom a space between a wall of a cylinder and the bellows as the bellowsis expanded.
 7. A pumping system according to claim 1 wherein eachcontrol device (30, 44, 46) comprises a respective piston and cylinderassembly.
 8. A pumping system according to claim 7 wherein the controldevices (30, 44, 98, 90 and 100) maintain a desired pressure balancebetween the hydraulic power medium and the medium which is pumped.
 9. Apumping system according to claim 2 wherein each control device (30, 44,46) comprises a respective piston and cylinder assembly.
 10. A pumpingsystem according to claim 3 wherein each control device (30, 44, 46)comprises a respective piston and cylinder assembly.
 11. A pumpingsystem according to claim 4 wherein each control device (30, 44, 46)comprises a respective piston and cylinder assembly.
 12. Pumping systemaccording to claim 5 wherein each control device (30, 44, 46) comprisesa respective piston and cylinder assembly.
 13. A pumping systemaccording to claim 6 wherein each control device (30, 44, 46) comprisesa respective piston and cylinder assembly.